(1) Field of the Invention
The present invention relates to a paper feed control method and, more particularly, to a paper feed control method which can maintain a high paper feeding precision of a paper sheet by a paper feed roller.
(2) Description of the Prior Art
Printers which can record characters, images, or the like on paper sheets by driving recording heads such as thermal heads, ink-jet heads are popularly used.
In such a conventional printer, while a paper sheet is transported between a platen and a printing head, the recording head is driven on the basis of recording information, so that characters, images, or the like are recorded on a paper sheet. A paper feeding apparatus in which a paper feed roller for transporting the paper sheet by a predetermined amount to perform a line feeding operation is arranged in the printer.
In a recent recording apparatus, image recording having more high quality is demanded. In order to perform image recording having high quality, an improvement in precision of a line feeding amount is demanded. For this reason, processing precision for the outside dimensions, deflection, and degree of roundness of the paper feed roller are improved, and production variations are reduced so as to improve the production quality of a paper feed roller itself or to devise paper feed control.
However, in order to improve the production quality of the paper feed roller itself to improve the precision of a line feeding amount in the conventional paper feeding apparatus described above, the paper feed roller requires an excellent processing precision, e.g., an allowance of a deflection precision of 5 .mu.m or less. The paper feed roller having an excellent processing precision has the following problems. That is, a yield of the paper feed roller is low, a lot of effort and long time are required to produce the paper feed roller, and an economical load is heavy.
When paper feed control is performed to improve the precision of a line feeding amount in the paper feeding apparatus, the paper feeding apparatus requires paper feed control which calculates a line feeding amount as a paper feeding amount required for a paper feeding operation, calculates a rotation amount of a paper feed motor for rotationally driving a paper feed roller on the basis of the outer periphery length or the like of the paper feed roller, and rotates the paper feed motor by the rotation amount to suppress variations in line feeding amounts.
As the paper feed control for suppressing the variations in line feeding amounts, control described in Japanese Unexamined Patent Publication No. 8-2032 is known. According to the paper feed control described in this publication, as shown in FIG. 6, a sensor roller 25 having an outer periphery length which is almost equal to the length of one line of a recording head is arranged in a paper feeding apparatus 1" such that the sensor roller 25 is in contact with a part of a paper sheet P transported by a paper feed roller 2. A sensor rotor 26 which is coaxially rotated with the sensor roller 25 is detected by a photosensor 27 to detect a paper feeding amount, and a paper feeding amount obtained by a paper feed motor 6 is controlled, so that a line feeding amount can be correctly determined.
However, the paper feeding apparatus has the following problems. That is, the sensor roller 25, the highly precise complex photosensor 27 for detecting a rotation amount of the sensor roller 25, and a control unit 31 for detecting a paper feeding amount from the rotation amount of the sensor roller 25 on the basis of a detection result of the photosensor 27 to control a paper feeding amount obtained by the paper feed motor 6 must be arranged in the paper feeding apparatus itself to increase the number of parts and to make an economical load heavy, so that a reduction in weight is hindered.
In addition, since the paper feeding apparatus causes the sensor roller to detect a line feeding amount every recording on a paper sheet, a line feeding operation requires a long period of time. In particular, a recent high-resolution paper feeding apparatus having a small line feeding amount has the following problems. That is, a line feeding operation requires a longer period of time, a recording rate decreases.
Furthermore, in recent years, as paper sheets used in recording, various types of paper sheets such as a plain paper sheet, a post card, an OHP paper sheet, an iron printing paper sheet, a seal paper sheet, and a dedicated paper sheet whose surface smoothness is improved are used. Since variations in line feeding amounts are caused by variations in contact pressures between a paper feed roller and paper sheets or the types of paper sheets used in recording, the following problems are posed. That is, an arithmetic process time in a control unit is long, a large-capacity memory is required, and software is inevitably large. As a result, a lot of effort and long time are required to develop the software, and an economical load is heavy.